1. Field of the Invention
The field of the present invention is lasers, and in particular lasers having output defined by a number of fixed frequency laser lines.
2. Background
The lasing medium of a variety of lasers produce an output characterized by a plurality of fixed frequency laser lines (also referred to herein as spectral lines). Such lasers include CO2 lasers, CO lasers, all of the molecular lasers operating on a number of vibrational-rotational transitions, and argon ion and other lasers that are capable of producing a number fixed frequency laser lines at discrete wavelengths. Generally, for any of these lasers, light output from only one of the laser lines is utilized at a time. If the laser is operating on more than one of the wavelengths at any given time, all of the other laser lines are filtered out with a wavelength selector, such as a grating spectrometer, band pass filter, or any other type of wavelength selector known to those skilled in the art. The unused laser wavelengths and their corresponding optical power output are discarded. This often results in wasted power and reduces the overall operating efficiency of the laser system. It is, therefore, desirable to have the laser amplify only one desired wavelength at any given time. For the molecular lasers such as the CO2 lasers, amplification of only one line results in all the power output from the laser occurring on the corresponding transition and results in increased efficiency of the laser for producing laser output at the desired wavelength. Thus it is desirable to have the wavelength selector inside the laser cavity rather than outside the cavity where the wavelength selector must select a given wavelength from the output of a laser operating on multiple transitions simultaneously. The internal wavelength selector is usually adjustable to allow light from any one of the laser lines to be selected for resonance in the cavity. If the absolute tuning position of the wavelength selector, for example the angle of the grating with respect to the lasing axis, as it relates to the actual wavelength selected, can be specified then the output of the system may be tuned directly to the desired wavelength by simply adjusting the wavelength selector. However, if the absolute position of the wavelength selector cannot be specified or the mechanical or thermal stability of the system cannot be assured for long periods of time, then additional equipment, and in some instances additional information, is needed to selectively tune the system to the desired wavelength.
One solution is to employ an external or internal spectrometer in combination with the wavelength selector. With this addition, the absolute position of the wavelength selector does not need to be known as the spectrometer may be used to track the wavelength of the light generated by the laser. However, even with this system substantial mechanical and thermal stability is required.
A second solution is to monitor the laser power output as a function of the tuning of the internal wavelength selector. While this solution does not require knowing the wavelength at or near the peak of the desired laser line, it does require knowing the absolute power output of the laser at the peak of each of the laser lines so that a specific laser line can be selected by knowing the absolute maximum power produced by the laser as a function of the tuning of the wavelength selector. This requirement gives rise to difficulties in using such a system with different lasers because absolute power at a particular laser line can vary significantly, even for similar types of lasers. Moreover, as a laser ages, even for a well-characterized laser, the absolute power output on a given transition cannot be guaranteed over the lifetime of the laser. Moreover, some of the laser lines may accidentally produce the same amount of output power.
Thus, an improved system and method for selecting an output wavelength from a laser is desired. Such an improved system and method should work with a wide variety of lasers having (1) a lasing medium that has an output characterized by a number of fixed frequency laser lines, and (2) an adjustable wavelength selector. The system and method should also require no prior knowledge of the laser""s absolute power profile and require no monitoring of the laser""s output wavelength to verify that the output wavelength is contained within the selected laser line.
The present invention is directed to a system and method for selecting an output wavelength of a laser, wherein the laser includes a lasing medium having an output spectrum characterized by a plurality of discrete spectral lines. The wavelength selection process ensures that the selected wavelength approximately corresponds to a peak of the desired spectral line. The system for selecting the laser wavelength comprises a laser having the qualities just described, an adjustable wavelength selector disposed within and optically coupled to the optical cavity of the laser, a detector optically coupled to the laser for monitoring the power of light output from the laser, and a processor electronically coupled to the wavelength selector and the detector.
The wavelength of light selectively passed by the adjustable wavelength selector resonates within the optical cavity and provides the necessary feedback for generating the output of the laser. Thus, light output from the laser is primarily comprised of the chosen wavelength. The power of the light output is measured by the detector and the power measurements are transmitted to the processor. The processor adjusts the wavelength selector through a series of discrete steps, receiving at least one power measurement at each of the steps. Statistical analyses are performed on the power measurements, and based on the statistical analyses, the processor adjusts the wavelength selector to selectively pass light having a wavelength that approximately corresponds to a peak of one of the spectral lines. The statistical analyses performed preferably include standard deviation analyses and curve fit analyses.
Preferably, the laser included in the laser systems according to the present invention include a lasing medium having an output spectrum characterized by a plurality of discrete spectral lines and a distinct flat region where no spectral lines produce laser gain. The above process may be broken down into three distinct phases. In the first phase, the flat region is identified by adjusting the wavelength selector through a first series of discrete steps, taking power measurements of the laser light generated as the wavelength selector is adjusted, and identifying the flat region of zero power output through statistical analyses of the power measurements. Once the flat region has been located, the second phase of the operation is performed to identify the desired spectral line. This is done by adjusting the wavelength selector through a second series of discrete steps, taking laser power measurements, and identifying the desired spectral line through statistical analyses of the power measurements. The last phase comprises adjusting the wavelength selector in discrete steps through the identified spectral line to selectively pass a wavelength approximately corresponding to the peak of the desired spectral line.
Accordingly, it is an object of the present invention to provide an improved system and method for selecting an output wavelength from a laser. Other objects and advantages will appear hereinafter.